Why on earth would you want to blow that kinda money on running ONE train into GCT? To make the Acela capable of running into GCT you need to do a whole lot more than merely bolt 3rd rail shoes to it's trucks. You're gonna need to completely change the electronics that handle traction. The GCT 3rd rail and the NYP catenary are nowhere near equal in voltage, GCT is a 750volts DC system, while NYP uses 11,500volts AC (as well as a 750vdc 3rd rail for LIRR, which as mentioned is physically incompatible with MN's 3rd rail), given that they use a now swiftly aging GTO Thyristor system, some physical tweaking of the traction supplies would be needed. To say it'd be difficult is an understatement, you'd have to find a way to get the shoes to retract or it'd be forever limited to service from GCT to Boston. If you really want fast GCT-BOS service, we'd do better to just order a single Acela with DC operation built into run that route, but that'd still be a rather poor idea.
Now, in terms of actually possible things, why can't MN or ConnDot order some ALP46s for service from New Haven to NYP after LIRR's East Side Access opens? Regardless of what Amtrak and LIRR say, there must be some slots that will open up, the NH line could slip a few peak hour express trains into NYP, possibly easing the load on the Lex in Midtown. On a slightly more farfetched note, it would be possible for ConnDot or MN to modify the german Class 189 loco in the same manner that NJT modified the Class 185 into the ALP46. The Class 189 is a push-pull loco from Siemens which is capable of running under 4 catenary systems, 1500vdc, 3000vdc, 15kv@17hz, and 25kv@50hz. NJT and BBD's ADTranz division adopted the Class 185 almost flawlessly for US operation, I think it'd be childs play to modify a locomotive with an exisisting DC capability into a US market dual-system loco. In this case it quite literally would be "Bolt 3rd rail shoes on, install beefier wire to traction supply, change software in IGBT" to account for the changes in 1500vdc cat to 750vdc 3rd rail. MN's NH operations would then have a locomotive capable of operation all the way to Boston if the need ever arose (Thanksgiving Service?), and with retracting shoes, of roaming the entire NEC, capable of bringing SLE service straight to GCT or of handling the NH line's expresses while not wasting MUs better used on local trains where their acceleration can best be used.